The invention is related to an actuator, comprising a housing which contains a screw mechanism and an electric motor which is driveably connected to the screw mechanism which provides a linear movement in response to a rotational movement of the electric motor, said screw mechanism comprising a screw and a nut one of which is supported rotatably with respect to the housing by means of an angular contact ball bearing, said screw by means of an intermediate coupling element engaging an actuating member, for transferring axial forces, said actuating member comprising a housing which contains a screw mechanism and an electric motor which is driveably connected to the screw mechanism which provides a linear movement in response to a rotational movement of the electric motor, said screw mechanism comprising a screw and a nut one of which is supported rotatably with respect to the housing by means of an angular contact ball bearing, said screw by means of an intermediate coupling element engaging an actuating member for transferring axial forces, said intermediate coupling element engaging the screw by means of an axial connection which allows radial movements.
Such actuator is known from WO-A-9603301. This prior art actuator, which is part of a brake calliper, has a screw mechanism which by means of a pivotal intermediate coupling element is connected to a brake pad. Upon actuation of the electric motor which drives said actuator, the brake pad is pressed against a brake disc. As a result, the intermediate coupling element will be loaded and displaced somewhat in transverse direction, which transverse displacements could hamper and destroy the screw mechanism. In an attempt to alleviate this problem, an intermediate coupling element has been applied which is bar-shaped, and which at both ends is pivotally engaging the brake pad and the screw of the screw mechanism.
Although such coupling element eliminates the transverse loads as occur in a stiff connection, still problems may arise. In an oblique position of the bar-shaped coupling element, the actuating forces have a transverse component which leads to an unfavourable loading in the screw mechanism.
The object of the invention is to provide a solution for this problem. This object is achieved in that the intermediate coupling element and the screw engage each other by means of essentially radial surfaces, which surfaces are mutually radially displaceable.
Even in case the brake pad, as a result of engaging the brake disc, would be loaded and displaced somewhat in transverse direction, the screw mechanism will only be loaded in axial direction. This favourable loading results from the fact that the intermediate element and the screw are uncoupled in radial direction (within certain boundaries). The intermediate coupling element and the screw engage each other by means of essentially radial surfaces, which surfaces are mutually radially slidable; also, the mutually radially displaceability is basically governed by frictional engagement.
A very stable embodiment is obtained in case the screw has a ring shaped abutment surface engaging a pressure intermediate coupling element having a corresponding abutment surface, which abutment surfaces are slidably with respect to each other.
In case a compression member is provided for pressing the abutment surfaces onto each other, a rattle-free construction is obtained. Said compression member acts between the pressure intermediate coupling and a cap which is connected to the screw. Preferably, the compression member is a conical washer (Belleville washer).
The cap has an aperture for the actuating member, which rests against the pressure intermediate coupling element, and is sealed with respect to the actuating member.
The actuator according to the invention is in particular fit for application of a roller screw spindle.